1. Field of the Invention
The present invention relates to a method for producing a metal mask for screen printing. More specifically, the present invention relates to a method for producing a metal mask for screen printing that includes steps of: forming opening portions for printing (hereinafter referred to as “opening”) via laser irradiation, and removing dross (burrs) deposited by the opening forming process.
2. Description of the Related Art
A “metal mask” formed with a pattern of openings that corresponds to the printing pattern on a metal plate such as stainless steel is employed in fields that require relatively detailed printing, such as solder paste printing or photoresist layering during a method for producing printed circuits, IC substrates, etc. Accordingly, when such a metal mask abuts the surface of the product to be treated, and a solder paste or ink paste is applied from the opposing surface with a squeegee, etc., printing is performed on the surface of the product to be printed with the paste, corresponding to the pattern of openings.
A metal mask employed in this type of screen printing is formed with openings that correspond to the printing pattern of the abovementioned metal plate. Accordingly, various conventional etching technologies may be employed as the method for forming this type of pattern of openings, such as melting by laser irradiation, electrolytic polishing, etching by chemicals, etc. However, with the current popularization of CAD and CAM, by controlling the trajectory of laser irradiation in accordance with a predesigned predetermined print pattern, via computer numerical control (CNC) that employs CAD data, etc., even complicated patterns of openings can be processed relatively easily. Accordingly, operations for forming the above-described openings via laser irradiation have been frequently employed in recent years.
However, in this type of opening formation via laser irradiation, the openings are formed by melting the metal plate at the positions of laser irradiation. Accordingly, a portion of the metal melted by laser irradiation is attached and hardened at an edge of an opening on the surface of the metal plate on the opposite side from the side that was irradiated, and the raised edge portions of the openings where burrs arise are referred to as the portions where “dross” is deposited (refer to FIG. 2).
Therefore, when a metal mask with dross deposits like this is employed in screen printing and the dross deposited surface thereof is employed as the surface to be in close contact with the product to be printed, the metal mask cannot be brought into close contact with the surface of the product to be printed. As a result, because of the space arising between the metal mask and the surface of the product to be printed, detailed printing cannot be conducted. Conversely, when the dross deposited surface is positioned on a side opposite to that of the surface to be printed, the inflow of the paste into the inside of the openings is inhibited by the dross, so that an accurate amount of solder paste or ink paste cannot be supplied.
Accordingly, when boring a metal mask via this type of laser irradiation, an operation for removing this dross is conducted after the openings are formed by laser irradiation.
However, one method for removing these dross deposits involves, for example, etching the surface of a metal mask by being immersed in a chemical such as ferric chloride, etc., or electro-polishing the surface, with a metal mask placed in an electro-polishing solution.
However, when the abovementioned method is employed, not only are the dross deposits removed, but the edge portions surrounding the openings formed in the metal mask are also etched and polished. Accordingly, because the post-processed openings become larger at the front and rear surfaces, and the hole diameter in the center portion is formed into a narrowed drum shape (bilaterally symmetrical conical notch), the narrowed central portion presents resistance against the passage of solder paste or ink paste through the openings, which impedes the supply of solder paste or ink paste.
Moreover, because the diameters are enlarged by etching the edges of the openings, the actual printed shape becomes larges than the intended printing shape. As a result, even if the openings are formed into a shape with corners, for example, a planar rectangular shape, etc., because these corners are removed by etching, etc., and formed into a rounded shape, the printing of an extremely detailed shape cannot be performed, so that the quality of the printing is decreased.
In addition, when performing the elimination of dross deposited by electro-polishing or chemical etching, a chemical such as an electro-polishing solution or an etching solution is employed. Accordingly, when these chemicals are directly disposed of, etc., they cause considerable stress on the environment.
In such cases, a treatment is required to detoxify these chemicals before disposal, with the expenses required for this treatment being passed on to the cost of the metal mask itself, which in turn increases the production cost.
Thus, in recent years, conversion from a chemical treatment that employs chemicals, etc., to a dry-type treatment that does not employ chemicals, etc., has been sought.
As a method for performing dross removal via such a dry-type treatment, a method for producing a metal mask is provided whereby the surface of the metal plate is ground by sandblasting after a predetermined pattern of openings is formed by laser irradiation (refer to Japanese Patent No. 3160084).
Moreover, in the metal mask production method described in the abovementioned Japanese Patent No. 3160084, the sandblasting is intended not only to remove the deposited dross, but also to provide a satin-like finish to the surface of the metal mask (refer to paragraph [0014] of the abovementioned Japanese Patent No. 3160084). Unlike this method, however, a method has also been proposed whereby, rather than forming a satin-like finish, a glossy or mirror-like finish is provided on the surface of the product to be treated via the ejection of an abrasive. As the abrasive for providing this glossy or mirror-like finish to the product to be treated, an elastic abrasive is provided in which abrasive grains are supported on the surface of a core consisting of an elastic body, or the abrasive grains are dispersed by being kneaded into the core consisting of the elastic body, etc. (Japanese Unexamined Patent Application Publication No. 2006-159402; Japanese Unexamined Patent Application Publication No. 2001-207160; and Japanese Patent No. 2957492).